1. Field of the Invention
The present invention relates to the field of potentiometers, and more particularly to a miniature single-turn potentiometer having improved reliability and performance.
2. Description of the Prior Art
Miniature single-turn potentiometers have been available in various forms for many years. Typically, such a potentiometer includes a substrate upon which a first annular track of resistance material is formed. A second annular track of conductive material is disposed concentric to the first track on the substrate. A conductive wiper is attached to a movable rotor. The rotor and wiper are arranged such that electrical contact is made between the conductive track and the resistive track by the wiper. Leads are arranged on the substrate connecting ends of the annular resistive track (which is not laid out as a full circle but rather resembles the letter C) and the annular conductive track. As the rotor is turned about its axis, the wiper simultaneously contacts the conductive track and the resistive track. As seen from the conductive leads, the relative resistance measured between the conductive annular track and one end of the C-shaped resistive track will vary in accordance with the distance from the end of the track to where the wiper is contacting the resistive track. Such arrangements are shown, for example, in U.S. Pat. Nos. 3,597,837, 3,729,817 and 3,869,789.
In the aforementioned patents the wiper generally takes the form of a solid piece of resilient conductive material, such as beryllium copper. However, it is known to improve the contact between the annular conductive track and resistive track through the use of a V-shaped wiper formed of a series of conductive wires arranged parallel to one another, such as shown in U.S. Pat. No. 4,114,132. Such an arrangement has the advantage that the wire tips are free to flex with respect to each other and thus are less prone to causing a bad connection due to surface irregularities in the conductive or resistive tracks.
However, the above-described arrangements wherein the resistive and conductive tracks are disposed concentric to one another on the same substrate suffer from the drawback that in a miniature (e.g. less than 1/2 inch) square potentiometer package there is very little room to apply both the conductive and resistive tracks concentric to one another. This means that the width of each track is relatively narrow and thus the amount of area available for contact with the wiper is small. This results in less reliable contact between the portions of the wiper contacting the resistive track and the conductive track.
U.S. Pat. No. 4,114,131 shows a type of potentiometer in which an annular resistive track and an annular conductive track are disposed on opposite sides of a rotor. This arrangement overcomes some of the difficulties associated with having the resistive and conductive tracks side by side on the same substrate. However, this potentiometer uses a rather complicated two-piece wiper arrangement for contacting the tracks on both sides of the rotor.
Another drawback of prior art potentiometer designs is that they generally include three or more wire leads or terminals which are brought out at right angles to the potentiometer package for connection with electrical circuit. While such an arrangement can be adapted for mounting a potentiometer either vertically or horizontally with respect to a printed circuit board by the simple expedient of bending the wire legs, such devices are not easily adapted for use with certain types of automatic electronic component assembly or insertion machinery. This is because the wire leads or terminals of the component must be precisely located with respect to openings provided in an electronic circuit board prior to insertion.
One type of automatic circuit board assembly device which is becoming more prevalent is one which utilizes electronic components which do not have leads formed on them at all--instead, small conductive areas are provided on the outer surface of the electrical device which are designed to be mated with corresponding conductive areas formed on the surface of the printed circuit board. The electrical component is bonded to the circuit board using any one of a number of well-known techniqes.
It would therefore be of great benefit if there were available a miniature potentiometer having a simple and reliable arrangement for making contact between a conductive track and a resistive track and which is adaptable for automatic mounting to a printed circuit board without the need for precisely locating external leads.